Method of producing a multi-turn coil from folded flexible circuitry

ABSTRACT

A multi-turn coil device comprising a flexible circuit board and a plurality of serially electrically coupled coils coupled to both sides of the flexible circuit board. The coils are formed such that when the circuit board is folded in an accordion manner, the coils are substantially aligned and have the same direction of current flow. The coils are serially coupled sequentially from front to back and back to front wherein the coupling of the coils is through a plated through hole in the flexible circuit board.

RELATED APPLICATIONS

This patent application claims priority under 35 U.S.C. 119(e) of theco-pending U.S. Provisional Pat. App. No. 60/921,220, filed Mar. 29,2007, entitled “PRIMARY ONLY CONSTANT VOLTAGE/CONSTANT CURRENT (CVCC)CONTROL IN QUASI RESONANT CONVERTOR,” which is hereby incorporated byreference.

FIELD OF THE INVENTION

The invention relates to a device for and method of manufacturingmulti-turn coils. More specifically, the invention relates to the use offolded flexible circuitry to form a multi-turn coil.

BACKGROUND OF THE INVENTION

There has long existed a need for multi-turn coils. Such multi-turncoils are used as electronic components in sensors, actuators, antennas,transformers, and in motors or alternators. The current state-of-the-artfor manufacturing multi-turn coils is to form a coil trace on a circuitboard. Typically, the coil consists of a spiral of conductive materialthat is printed, etched, or otherwise formed on a circuit board. Atwo-layer coil can be formed by forming a coil on one side of the boardthat is coupled to a coil on the opposing side of the circuit board.What is needed is a low-cost multi-turn coil that is simple and acost-effective method to manufacture a coil with more than two layersand a larger number of coil turns.

SUMMARY OF THE INVENTION

In the first aspect of the invention, a multi-turn coil device isdisclosed. The device includes a flexible circuit board and a pluralityof coils coupled to the circuit board. The coils are coupled togetherserially and each coil has either clockwise or counter clockwise currentflow direction. Further, the coils have either an inward spiral oroutward spiral orientation. The coils are formed on the circuit boardsuch that when the flexible circuit board is folded, the coilssubstantially overlap each other and form a multi-turn coil. Preferably,the coils are formed such that when the flexible circuit board is foldedalong folding lines, the overlapping coils have the substantially thesame current flow direction.

The coils can be coupled, formed, or attached on one side or both sidesof the flexible circuit board. Preferably, there are coils on both sidesof the flexible circuit board and there are equal number of coils oneach side of the circuit board. Further, the coils on opposing sides ofthe board are preferably substantially aligned. The coils can be coupledtogether in any serial order. However, it is preferable that front andback opposing coils are sequentially and serially coupled together. Thisprovides a topology where the connections between coils do not have tocross any coil loops. The front side loop spirals towards the center andpasses through the circuit board where it couples to the back-side coil.The back-side coil spirals away from the center terminating at theoutside edge where it can be coupled with the adjacent back side coil.This layout of the coils eliminates the need for the coil paths to crossa coil trace or connector between the coil traces. The preferredsequence of serially coupling the coils is the repeating sequence frontto back and the back to front. The coupling of the coils on opposingsides of the board is preferably a conductive path through the circuitboard but other conductive paths are contemplated. The conductive pathcan be a connector or preferably a plated through hole. The flexiblecircuit board can be a single layer board or alternatively a multilayerboard can be used.

Before the flexible circuit board is folded and the coils aligned,insulation should be placed over the coils that are immediately adjacentto other coils after folding and thus prevent the coils from shorting.The insulation can be a coating applied to the coils. Alternatively, theinsulation can be a membrane or a number of membranes coupled to thecoils that will come into contact with another coil upon folding.

In another embodiment of the invention, the flexible circuit boardincludes means for aligning the coils when folding the circuit board.The alignment mean is preferably a folding line but other alignmentmeans are contemplated. These means can include but are not limited toalignment holes, markings on the circuit board, and patterns formed inthe flexible circuit board. The folding lines are preferably scoringlines on the flexible circuit board but can include other means such butnot limited to perforations, cuts, and indentations. The folding lineshould not cut or damages any conductive traces that transect thefolding line. The scoring lines can be formed on the circuit board, onthe insulation that is coupled to the circuit board, or both.

Different folding patterns can be used to form a multi-turn coil.Preferably an accordion pattern is used but other folding patterns arecontemplated by this invention. A fold over pattern can be used. Thisfolding pattern is formed by folding the flexible circuit board in halfand then again folding the circuit board in-half. Alternatively a doublefold can be use to fold the circuit board. In this pattern, the flexiblecircuit board ends are folded to the middle. Next, this folded structureis folded in-half. Also, considered is a roll over folding pattern. Thisfolding pattern is formed by folding the first coil or opposing coilpair onto the adjacent coil or coil pair. The folded structure isrepeatedly folded onto the adjacent coil or coil pair until all of thecoils are formed into in a multi-layer stack forming a multi-turn coil.

In a second aspect of the invention, a method of manufacturing amulti-turn coil device is disclosed. In one step a flexible circuitboard is formed. The circuit board can be any non-conductive flexiblematerial, preferably a polymer material, where the circuit board is cutfrom a larger sheet of polymer material. Alternatively a flexiblenon-conductive material could be poured into a mold or rolled out toprovide the desired flexible circuit board shape.

In another step multiple coils are formed and coupled to the flexiblecircuit board. The coils can be formed by the method of but not limitedto etching, electroplating, or adhesively coupling preformed coils tothe flexible circuit board. Alternatively, the coils can be formed byprinting with electrically conductive ink. Preferably, the coils arepositioned to substantially overlap when the flexible circuit board isfolded. Further, the circuit flow direction of each coil, eithersubstantially clockwise or counterclockwise, is preferably all in thesame direction.

As part of the manufacturing of the multi-turn coil, an alignment meanscan be formed on, coupled to, or attached to the board. The alignmentmeans includes but are not limited to a hole through which a mechanicaldevice provides alignment, forming circuit board structures thatinterlocks to provide alignment, applying marks to help an externalalignment mechanism, or preferably forming a folding line. A foldingline can be formed by perforations, cutting, marking, or preferablyscoring. The folding line should not interfere with any conductors thattransect the folding line. Such interference includes cutting, damaging,or substantially increasing the resistance of the conductors transectingthe folding line.

For a multi-turn coil, with coils on both sides of the flexible circuitboard, a means is needed to serially couple the coils on the front sideof the flexible circuit board and the back side of the flexible circuitboard. Preferable, the coupling is through an electrically conductivepath through the board. One method for such a coupling is with platedthrough holes however other methods are contemplated. These can includebut are not limited to a connector or wires.

Before folding the flexible circuit board with the coupled coils,insulation needs to be applied to the coils that will come into contactwith another coil upon folding and thus short. This insulation can be acoating formed onto the coils. Alternatively, the insulation can be aninsulating membrane that is coupled to the coils or other conductorsrequiring that will come into contact upon folding. Single or multiplepieces of insulation can be used. The placement of the insulation willdepend on the folding pattern used.

In one embodiment, the preferred method for folding is an accordionpattern. However, other folding patterns are contemplated. These foldingpatterns include but are not limited to a fold-over pattern, adouble-fold pattern, or a rolling-fold pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is better understood by reading the following detaileddescription of exemplary embodiments in conjunction with theaccompanying drawings.

FIG. 1A is a top view illustration of a flexible circuit broad withcoils serially connected on both sides of the circuit board connect fromone side to the opposing side through a plated through hole.

FIG. 1B is a top view illustration of a flexible circuit broad withcoils serially connected on a single side.

FIG. 1C illustrates a side view of a flexible circuit board withserially connected coils on both sides of the board with an insulationcoating on the top and bottom of the board.

FIG. 2 illustrates the multi-turn coil where the flexible circuit boardis partially folded in an accordion manner and with an insulationmembranes.

FIG. 3 illustrates a multi-turn coil where the flexible circuit boardand insulation membranes, folded with an fold over pattern.

FIG. 4A illustrates an alternative circular coil geometry.

FIG. 4B illustrates an alternative elliptical coil geometry.

FIG. 5 illustrates a flow chart of the inventive steps for forming amulti-turn coil.

DETAILED DESCRIPTION OF THE INVENTION

The following description of the invention is provided as an enablingteaching of the invention in its best, currently known embodiment.Persons skilled in the relevant art will recognize that many changes canbe made to the embodiment described, while still obtaining thebeneficial results of the present invention. It will also be apparentthat some of the desired benefits of the present invention can beobtained by selecting some of the features of the present inventionwithout utilizing other features. Accordingly, those who work in the artwill recognize that many modifications and adaptions to the presentinventions are possible and may even be desirable in certaincircumstances, and are a part of the present invention. Thus, thefollowing description is provided as illustrative of the principles ofthe present invention and not in limitation thereof, since the scope ofthe present invention is defined by the claims.

FIG. 1A illustrates an unfolded multi-turn coil 100 formed from aflexible circuit board 110 with a series of inwardly spiraling coils 120and outwardly spiral coils 125. Once folded, the multi-turn coil 100 canbe used as part of a sensor (not shown).

In the shown embodiment, a number of inwardly spiraling coils 120 andoutwardly spiraling coils 125 are shown on the front and back side ofthe flexible circuit board 110. The coils 120 and 125 on the back sideof the circuit board 110 are shown with dashed lines. The coils 120 and125 are connected serially. The connection between a coil 120 on thefront of the board 110 and the opposing coil 125 on the back of thecircuit board 110 is provided by a plated through hole 130. However,other methods of providing connectivity are contemplated including butnot limited to direct soldering, connectors, and wires.

To produce a device that is sensitive to magnetic flux, the flowdirection of the circuit path of the coils 120 and 125 need to be in thesubstantially same direction when folded. The flow direction refers toeither a clockwise or counter clockwise current flow in the coils 120and 125. Thus, the current flow direction of the coils 120 on the frontof the circuit board 120 and the opposing coils 125 back of the circuitboard 110 must be formed and coupled to maintain a substantially similarcurrent flow direction in relation to a magnetic field passing throughthe center of the coils 120 and 125.

Following the circuit path shown in FIG. 1A, the circuit starts from thecontact point 150 and is coupled coil 120 on the front side of theflexible circuit board through the conduction path 122. The coil 120 andcircuit path follows a substantially clockwise direction whichterminates at the plated through hole 130. The plated through hole 130is located inside of the coil path. The circuit path continues throughthe flexible circuit board 110 to the back side of the board 110 by theway of a plated through hole 130. On the back side of the board, theplated through hole 130 is coupled to the coil 125. The flow path forthe coil 125, on the back side of the circuit board 110, follows in asubstantially clockwise outward spiral direction, as viewed from the topside of the circuit board 110. The back-side coil 125 terminates on theoutside edge of the coil 125 where it is then coupled by a conductor 124to the adjacent coil 120.

The coils 120 and 125 are preferably coupled in the repeating pattern offront to back and then back to front. This coupling arrangement has theadvantage of being able to couple to the adjacent coil without having tocross a coil conductor. As shown, the back-side coil 125 spiralsoutwards in a clockwise direction, as viewed from the top, to theconductor 124 which connects the adjacent coil 120 on the backside ofthe circuit board 110.

Preferably, the flexible circuit board 110 is designed to fold in anaccordion manner. The pairs of coils 120 and 125 in adjacent foldingsections are formed in a mirror image of the adjacent coils 120 and 125.Further, the coils are formed or placed on the flexible circuit board110 such that when the flexible circuit board 110 is folded in anaccordion manner, the adjacent coils 120 and 125 are substantiallyaligned and each coil 120 and 125 has the same current flow direction.

The circuit path ends at the connection point 152. The connection point152 is shown on the top side of the flexible circuit board 110 but otherlocations are contemplated. A plated through hole (not shown) could beadded and the contact 152 positioned formed on the opposing side of theflexible circuit board 110. The contact point 152 could be run to anyplace on the board 110 that does not interfere with the operation of thecoils 120 and 125. Preferably the contact points 150 and 152 areconfigured for a solder joint. Other circuit coupling means arecontemplated such as but not limited to eutectic bonds, or a connector.

Alignment of the coils 120 and 125 is assisted by the forming of foldinglines 140. Preferably the folding lines 140 are a series of scores inthe flexible circuit board 110 or alternatively in an insulation layer,or both. Preferably, the scoring does not damage or increase theresistance of the electrical conductors 122 and 124 between adjacentpairs of coils 120 and 125 or any other conductors that transect thefolding line 140. Further, the folding lines 140 are positioned so thatthe pairs of coils 120 and 125 are aligned once folded in an accordionpattern. Other means to create a folding line 140 are also contemplated.These means include but are not limited to the flexible circuit board110 being perforated or partially cut.

For illustrative purposes, the coils 120 and 125 on the back side of theboard 110 are shown slightly offset. Preferably, the coil 120 on the topside and the bottom side are substantially aligned. Alignment increasesthe sensitivity to a magnetic flux passing through the center of thecoils 120 and 125.

FIG. 1B illustrates an alternative embodiment of an unfolded multi-turncoil 100′ formed from a flexible circuit board 110′ with a series ofcoils 120 and 125 on a single side of the circuit board 110′. Aone-sided multi-turn coil 100′ can provide the advantage that of beingeasier to manufacture. Like the coils 120 in FIG. 1A, adjacent coils areformed in a mirror image of each other so that when the circuit board isfolded in an accordion pattern, each coil has the same circuit flowdirection. Further, the coils 120 and 125 are serially couple withconnectors 122 and 124 so that the each coil 120 and 125 has the sameflow direction when the circuit board 110′ is folded. The coupling ofthe coils can require a bridging component 160 to cross from the insideof the coil 120 to the outside of the coil 125. The bridging component160 should not cause any electrical shorts across the coils 120 and 125.A short would greatly reduce the sensitivity of the coils 120 and 125 toa magnetic flux. The bridging component 160 can be an electricallyconductive wire or trace with insulation 165 configured to preventshorting to the coil. Alternatively, the bridging component could be atrace (not shown) on the backside of the board 110′ or a trace with in amulti-layer flexible circuit board, coupled to the coils 120 and 125 bya through hold (not shown).

The folding lines 140 and the connection points 150 are as described forthe corresponding items in FIG. 1A. The connection points 150 and 152can be positioned on either side of the circuit board 110′ or at anypoint on the board that does not interfere with the operation of thecoils 120 and 125.

FIG. 1C illustrates a side view of the unfolded multi-turn coil 100″with coils 120 and 125 on both sides of the flexible circuit board 110.Additionally, an insulation layer 170 and 180 is shown on the top andbottom of the circuit board 110. The insulation layer 170 and 180prevents the coils 120 and 125, and the connectors 122 and 124 fromshorting when folding the flexible circuit board 110. The insulationlayer 170 and 180 is shown as a coating on the top and bottom of theboard. However, other means for providing insulation is contemplated.These means include but are not limited to a single membrane (not shown)covering both sides of the unfolded multi-turn coil 100, or individualmembranes (not shown) covering a sufficient area of coils 120 and 125 toprevent shorting. An adhesive or mechanical device (not show) can beused to hold the device 100″ in a folded and aligned configuration.

FIG. 2 illustrates an accordion folded two sided multi-turn coil 200.The device structure is as described for 100-FIG. 1A with the additionof the insulation membranes 280 to prevent the coils 120 and 125 onadjacent folds from shorting together. Preferably, the membranes 280 areas thin as possible. As illustrated, the multi-turn coil 200 is notfully configured. In a final configuration the multi-turn coil 200 doesnot have a gap between the insulator 280 and the coils 120 and 125.There can be some coupling material, such as an adhesive, between thecoil 120 and 125 and the insulators to hold the device 200 in a foldedand aligned configuration. Alternatively, a mechanical device can beused to hold the device 200 in the folded configuration.

FIG. 3 illustrates an alternative method for forming a multi-turn coil300. As illustrated a fold over technique is used to form the multi-turncoil 300. In the fold-over technique, the unfolded multi-turn assembly100-FIG. 1 is folded in half, and then folded in half again and againuntil all the coils substantially overlap. The device structure is asdescribed for 100-FIG. 1A with the addition of the insulation membranes380 and 382 to prevent the coils 120 and 125 on adjacent layers fromshorting together. The resulting multi-turn coil 300 preferably has thecircuit flow direction of the coils 120 and 125 orientated in the samedirection.

While two folding techniques are illustrated in FIG. 2 and FIG. 3, otherfolding techniques are contemplated. These include a double fold wherethe ends are folded into the middle and then folded in half. Thispattern is repeated until all the coils substantially overlap. Also,roll folding is contemplated where the flexible circuit 110-FIG. 1 alongwith an insulation membrane 380-FIG. 3 is repetitively folded over onitself. To form a multi-turn coil with the coil orientations having thesame flow direction, these folding techniques can require a differentarrangement of the coils 120 and 125 and the connections between thecoils.

FIGS. 4A and 4B depict alternative embodiments of the coils. In FIG. 4A,the coil is circular. The coil conductor 410 is shown spiraling inwardsbut can also be a coil that spirals outward. The coil ends at a couplingpoint 420 which can be but is not limited to a plated through hole 420.The coil can be formed of any conductor or semiconductor, preferablycopper.

In FIG. 4B, the coil is an elliptical or race track shape providing ashaped response pattern to electrical and magnetic fields. The conductor410′ of a coil is shown spiraling inwards but can also be a coil 410that spirals outward. The coils end at a coupling point 420 which can bebut is not limited to a plated through hole 420. The coil can be formedof any conductor or semiconductor, preferably copper. The coil shapescan be changed for packaging reasons or for shaping a response ortransmission pattern of the multi-turn coil.

FIG. 5 shows a block diagram of the inventive steps of manufacturing amulti-turn coil 500. The method begins at the formation of a flexiblecircuit board 510. The board can be formed of any commonly used materialfor forming flexible circuit boards including but not limited topolymers. The flexible circuit board can be a multi-layer board withcircuit traces formed to support functions other than the multi-turncoil. Where through holes are used to electrically couple coils, therequired through holes can be formed in this step.

In the step 520, the coils are formed and coupled to the flexiblecircuit board formed in step 510. Preferably the coils are formed byplating a copper base on the flexible circuit board and etching thetraces. However, other techniques are contemplated including but notlimited to attaching preformed coils to the flexible circuit board orprinting the coils with electrically conductive ink. The coils can beformed and coupled on a single side, both sides or can be containedwithin the layers of the flexible circuit board. The formation of thecoils can also form the electrical connections through the flexiblecircuit board (the plated through holes) and the connections between thecoils. Further, if an electrical conductor or trace transverses anotherconductor, the step includes the formation of an insulation barrier toprevent shorting between the conductors.

In the optional step 530, an alignment structure is formed. Thealignment structure assists in the alignment of the coupled coils suchthat the coils are substantially overlapping and the all have the samecircuit flow direction. The alignment structure is preferably a foldingline that is formed by scoring the flexible circuit board while notdamaging the traces that transect the fold line. Other methods offorming a folding line are contemplated. These include but are notlimited to perforations, or cuts in the flexible circuit board. Otheralignment structures are contemplated including but not limited toalignment holes, indentations, and alignment markings for externalmachines or operators to use for alignment.

In the step 540, insulation is coupled to at least the coils that willcome into contact with other coils or electrical traces when folded.Preferably, the coating is a membrane that is glued to the coils beforethe flexible board is folded. Alternatively, the membrane can be held inplace by pressure of the folded circuit board. The insulating membranecan be individual pieces for each coil needing insulation, a singlemembrane for each side, or a single membrane that substantially wrapsthe entire flexible circuit board with the coupled coils. Apertures canbe formed in the membrane for the contact points on the multi-turn coil.Also, within the contemplation of the invention, is the application ofan insulation coating to both sides of the board. The method of applyingthe insulation includes but is not limited to spraying or dipping themulti-turn assembly into an insulation material. The insulation materialmay require drying or curing after application. Preferably theinsulation material is flexible and does not impede the folding of theflexible circuit board and coils.

In the step 550, the flexible circuit board with the coupled coils isfolded to form a multi-turn coil. Preferable, an accordion fold is usedbut other folding patterns are contemplated. These patterns include butare not limited to a fold over pattern, a double fold, and a roll fold.The fold over pattern has the circuit board folded in-half, and again inhalf. The double fold patterns has the ends folded towards the middleand then this structure is folded in-half. For a roll fold, a coil onone end is folded over onto the adjacent coil. These fold patterns arerepeated until all the coils are substantially aligned and therebyforming a multi-turn coil.

Other folding patterns are contemplated. Additionally geometries otherthan a linear coil are contemplated. Folding patterns could be used tocreate a toroid-shaped coil.

1. A multi-turn coil device comprising: a. a flexible circuit board; andb. a plurality of serially electrically coupled coils coupled to theflexible circuit board, each coil having a coil direction, and whereinthe coils are positioned such that each coil substantially overlaps eachof the other coils when the flexible circuit board is folded.
 2. Thedevice of claim 1, wherein the coils are configured so that when theflexible circuit board is folded, each overlapping coil is insubstantially the same direction.
 3. The device of claim 2, wherein theflexible circuit board has a first side and a second side and whereinone or more coils are coupled to the second side.
 4. The device of claim3, wherein the serially electrically coupled coils on the first side areelectrically coupled to the coils on the second side through anelectrically conductive path through the flexible circuit board.
 5. Thedevice of claim 2, wherein the folding circuit board is a multilayerflexible circuit board.
 6. The device of claim 2, further comprising aninsulator configured to prevent the shorting of the coils when folded.7. The device of claim 2, further comprising one or more alignmentmeans.
 8. The device of claim 7, wherein the alignment means is afolding line.
 9. The device of claim 2, wherein the flexible circuitboard if folded according to an accordion fold, a fold over fold, adouble fold, or a rolling fold, therein forming a multi-turn coil.10-20. (canceled)